tailieunhanh - SOIL ENGINEERING: TESTING, DESIGN, AND REMEDIATION phần 4

Không giống như một số dự án của chính phủ vượt chi phí có thể được dung thứ, tư vấn kinh doanh có tính cạnh tranh cao, chi phí quá mức thường dẫn đến tổn thất tài bị xáo trộn có thể được thu thập trong quá trình khoan. Đôi khi chúng có thể được thu thập mà không gián đoạn các hoạt động. Mẫu có thể được thu thập từ hom khoan khoảng thời gian. Các kỹ sư hiện trường | Upon completion of excavation the stress condition in the soil mass will undergo changes. There will be elastic rebound. Stress releases increase the void-ratio and alter the density. Such physical changes will not take place instantaneously. If construction proceeds without delay the structural load will compensate for the stress release. Thus this will not be a significant amount. Permeability The permeability of the soil determines the rate of ingress of water into the soil either by gravitational flow or by diffusion and these in turn determine the rate of heave. The higher the rate of heave the more quickly the soil will respond to any changes in the environmental conditions and thus the effect of any local influence is emphasized. At the same time the higher the permeability the greater the depth to which any localized moisture will penetrate thus engendering greater movement and greater differential movement. Therefore the higher the permeability the greater the probability of differential movement. Extraneous Influence The above-mentioned basic factors although difficult to predict can be evaluated theoretically. At the same time extraneous influences are totally unpredictable. The supply of additional moisture will accelerate heave for instance if there is an interruption of the subdrain system to allow the sudden rise of a perched water table. The development of the area especially residential construction can contribute to a drastic rise of the perched water table. Various methods have been proposed to predict the amount of total heave under a given structural load. These include the double oedometer method the Department of Navy method the South Africa method and the Del Fredlund method. Recently with the advance of suction study Johnson and Snethen claimed that the suction method is simple economical expedient and capable of simulating field conditions. Some fundamental differences between the behavior of settling and heaving soil are as .